The overall objectives of this proposal are to elucidate the molecular basis for the regional differences in the function of the plasma membrane of mammalian spermatozoa and to determine how the development modifications of the sperm membrane which occur during maturation in the epididymis and during capacitation relate to the spermatozoon's ability to fertilize on ovum. The biochemistry and ultrastructure of the plasma membrane of intact spermatozoa and isolated sperm membrane fractions will be studied with the following specific objectives: 1) The structure of different regions of the plasma membrane will be analyzed by freeze fracture, negative stain, optical diffraction, and specific surface probes. 2) The molecular mechanisms responsible for forming the paracrystalline intramembranous particle arrays in the sperm plasma membrane will be investigated by electron microscopy and by extraction/reconstitution experiments monitored by electron microscopy. 3) Regional variations in the molecular composition of the plasma membrane will be determined by cell fractionation, SDS polyacrylamide gel electrophoresis, and electron microscopy; integral and peripheral membrane proteins will be identified by extraction experiments monitored by electron microscopy. 4) Biochemical changes in the sperm plasma membrane during epididymal maturation and capacitation will be assessed by direct biochemical analysis and by the use of specific surface probes to radioactively label externally disposed membrane proteins. 5) The site of synthesis of membrane proteins which appear on the sperm surface during epididymal maturation will be determined using monospecific antisera against membrane proteins in conjunction with fluorescence microscopy. 6) The role of the epididymis ad androgens in the developmental modification of the sperm plasma membrane will be studied using antiandrogens in intact animals and also by using organ cultures of epididymal tubules and their sperm contents under defined culture conditions.